Underground extraction methodology of contiguous coal seams ensuring the safety of the parting and the surface structures

Abstract

In India, the coal seams are called contiguous, when the thickness of the parting formation between two coal seams is within 9 m. When the extraction is carried out in one seam, it not only disturbs the stress regime of the current working and its adjoining mined out areas but also alters the stress regime of the overlying and underlying formations. The interactions among coal seams become more pronounced when the thicknesses of the partings are lesser. If the parting between two coal seams collapses during their extractions, there may be a chance of casualty. The extraction of the contiguous seams becomes more difficult if the surface structures are present above the seams. If the seams are situated at a shallow depth of cover, the effects of the contiguous seams working easily reach to the ground surface. Therefore, the contiguous coal seams require suitable extraction methodology to ensure safety. In this study, a methodology is designed for safe extraction of the contiguous coal seams under surface structures. The safety of the parting is assessed by the analytical models, the numerical simulations and field investigation. The support system is designed to ensure the safety of the parting during the extraction of the coal seams. To assess the impact of mining on the surface structures, subsidence parameters are evaluated which are found to be within the permissible limits. Thus, this extraction methodology and the safety control measures can be applied for safe extraction of the contiguous coal seams having similar geomining conditions.